Ethene, gibberellins and hormone uses in plants
Homeostasis and response • Plant hormones (biology only)
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Ethene (C2H4)
Ethene functions as a gaseous plant hormone that diffuses between tissues and between fruits. Cause: Ethene production increases in ripening or damaged fruit and in rotting fruit. Effect: Ethene triggers biochemical changes that convert starches to sugars, soften cell walls and change colour, producing rapid ripening. Ethene is present in high concentrations in rotting fruit and can induce ripening in nearby fruit by diffusion, so proximity to ethene sources accelerates ripening and decay . Higher-tier detail: Ethene also controls cell division and helps flowers open, and it participates in leaf abscission .
Gibberellins
Gibberellins form a group of hormones involved in stem elongation, breaking seed dormancy and initiating germination. Cause: Gibberellin levels increase in seeds when environmental conditions become favourable. Effect: Gibberellins stimulate metabolic processes that resume embryo growth and mobilise food reserves, allowing the radicle to emerge and germination to proceed . Higher-tier detail: Gibberellins are used commercially to end seed dormancy and to increase fruit size and flowering under controlled conditions .
Auxins and their agricultural/horticultural uses
Auxins promote cell elongation and direct growth responses such as phototropism and gravitropism. Cause: Localised auxin concentration differences produce differential growth rates in tissues. Effect: Auxins encourage root formation when applied to cuttings and control directional growth in shoots. Practical uses: Auxins in rooting powders speed root formation in cuttings; synthetic auxins in selective weedkillers cause uncontrolled growth in broadleaved weeds, killing them while leaving narrow-leaved grasses largely unaffected due to leaf-surface absorption differences . Tissue culture and artificial propagation use auxins to induce root or shoot formation in cloned plants .
Practical uses of ethene and gibberellins
Ethene is applied to ripen fruit that were harvested unripe for transport. Cause: Application of ethene gas or ethene-releasing treatments initiates ripening reactions. Effect: Fruit begin to ripen shortly before sale, reducing transport losses and ensuring edible fruit on shelves . Gibberellins are applied to seeds or seedlings to break dormancy and promote germination, to stimulate flowering in some crops and to increase fruit size where required .
Limiting factors and cautions
Limiting factor: Timing of hormone application determines effectiveness; premature application of ethene causes spoilage during transport. Limiting factor: Concentration matters; excessive auxin exposure may damage desired plants or reduce biodiversity when used as broad applications. Environmental and economic considerations: Selective weedkillers reduce weed competition but can affect non-target species and soil ecosystems; hormone treatments require regulation and careful dosing to avoid crop loss or reduced shelf life .
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